In the past, conventional dewatering or drying methods have employed heat application such as distillation, evaporation, or freezing methods to remove water from sludges and slurries of wet solids. The cost of such processes is high because in the distillation and evaporation processes a substantial amount of heat is required and in the freezing processes a temperature reduction to 32.degree. F. or less is required, necessitating large amounts of heat exchange surface area. Heat application processes also volatilize any volatile matter of the solids to be dewatered.
It is known, for example, that peats, lignites and sludges contain dry solids contents of 2-70 percent by weight and that the dry solids, can have a thermal content (heating value) ranging from 2,500 to 14,000 BTU per pound. It is also known that the volative matter in these sludges may range from 30 to 90 percent by weight of the total dry solids content and that heat treatment processes to concentrate these solids from their water admixture, volatilize these volatile materials causing loss of thermal content and other values and creating odors and sometimes creating noxious chemicals.
Utilization or disposal of the wet sludges by combustion or incineration requires large quantities of supplementary fuel to vaporize the water content of these sludges and raise the steam so produced, to combustion or incineration temperatures.